Incorrect minimum supported rust version

[hoxxep]

Using cargo msrv suggests that the actual minimum supported rust version is 1.66.1 due to the following compile failure in the jobserver v0.1.27 sub-dependency required by the cc/parallel feature.

Check for toolchain '1.64.0-aarch64-apple-darwin' failed with:
┌──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ Compiling libc v0.2.150                                                                                                                                          │
│    Compiling pkg-config v0.3.27                                                                                                                                  │
│    Compiling zstd-safe v7.0.0 (/Users/liam/RustroverProjects/zstd-rs/zstd-safe)                                                                                  │
│    Compiling jobserver v0.1.27                                                                                                                                   │
│ error[E0412]: cannot find type `RawFd` in `std::os::fd`                                                                                                          │
│  --> /Users/liam/.cargo/registry/src/github.com-1ecc6299db9ec823/jobserver-0.1.27/src/error.rs:2:27                                                              │
│   |                                                                                                                                                              │
│ 2 | type RawFd = std::os::fd::RawFd;                                                                                                                             │
│   |                           ^^^^^ not found in `std::os::fd`                                                                                                   │
│   |                                                                                                                                                              │
│ help: consider importing this type alias                                                                                                                         │
│   |                                                                                                                                                              │
│ 1 | use std::os::unix::prelude::RawFd;                                                                                                                           │
│   |                                                                                                                                                              │
│ help: if you import `RawFd`, refer to it directly                                                                                                                │
│   |                                                                                                                                                              │
│ 2 - type RawFd = std::os::fd::RawFd;                                                                                                                             │
│ 2 + type RawFd = RawFd;                                                                                                                                          │
│   |                                                                                                                                                              │
│                                                                                                                                                                  │
│ error[E0603]: module `fd` is private                                                                                                                             │
│  --> /Users/liam/.cargo/registry/src/github.com-1ecc6299db9ec823/jobserver-0.1.27/src/error.rs:2:23                                                              │
│   |                                                                                                                                                              │
│ 2 | type RawFd = std::os::fd::RawFd;                                                                                                                             │
│   |                       ^^ private module                                                                                                                      │
│   |                                                                                                                                                              │
│ note: the module `fd` is defined here                                                                                                                            │
│                                                                                                                                                                  │
│ Some errors have detailed explanations: E0412, E0603.                                                                                                            │
│ For more information about an error, try `rustc --explain E0412`.                                                                                                │
│ error: could not compile `jobserver` due to 2 previous errors  

Submitting a matching PR to bump msrv in Cargo.toml.

[gyscos]

This looks like it's caused by jobserver 0.1.27, not by this crate itself. You might be able to downgrade the version used by your application by including jobserver = "<0.1.27" in your Cargo.toml. With this, this properly compiles on rustc 1.64.0.

[hoxxep]

I have submitted an MR to jobserver (rust-lang/jobserver-rs#62), so that it will no longer cause a breaking change in this crate's MSRV. If that gets merged I'll close this issue and the associated PR 👍

[epage]

FYI non-semver upper bounds are generally discouraged as they can create incompatibilities between crates. The proper way to handle this would be in Cargo.lock which can be edited with cargo update.

[hoxxep]

Closing this issue as @epage and @dtolnay have pointed out there are workarounds and an MSRV-aware dependency resolver in Cargo would be the real solution. I'll leave the jobserver MR open for the crate owners to decide upon, as the change should be trivial there to support a lower MSRV.

[gyscos]

One problem is also that jobserver 0.1.27, the offending version, does not specify a MSRV at all (it was only added right after that version was published), so a MSRV-aware cargo would not be able to do much here.